1. Field of the Invention
This invention relates to improvements in a vapor treatment system incorporated with a storage tank for volatile liquid such as gasoline, kerosene benzene and alcohol, more particularly to a fuel vapor treatment system incorporated with a fuel storage tank containing fuel.
2. Description of the Prior Art
Most gasoline-fueled automotive vehicles have been equipped with an emission control or vapor treatment system to prevent gasoline vapor from being emitted to the atmospheric air from the viewpoint of environmental protection. Such gasoline vapor is mainly generated in a gasoline storage tank during stoppage or running of the vehicle. An example of such an emission control system is shown in FIG. 6 to be incorporated with the gasoline storage tank 1. The emission control system includes a carbon canister 2 which is connected through a first ventilation line R1 with an upper space inside the storage tank 1. The first ventilation line R1 is provided with a check valve 3 for the purpose of maintaining the pressure inside the storage tank 1 within a predetermined range. The check valve 3 is adapted to allow gasoline vapor to pass therethrough when a positive pressure is prevailing in the storage tank, while to allow air to pass therethrough when a negative pressure is prevailing in the storage tank. During stoppage or running of the vehicle, gasoline vapor generated inside the storage tank 1 is fed through the first ventilation line R1 into the carbon canister 2 filled with activated carbon, so that the gasoline vapor is adsorbed in the activated carbon. This is a so-called charge mechanism for gasoline vapor.
A fuel supply pipe 1a of the storage tank 1 is provided with a partition valve 4 which is adapted to be opened and closed upon insertion and extraction of a fuel supply nozzle N. When this partition valve 4 is opened, the inside of the fuel supply pipe 1a is connected through the partition valve 4 and a second ventilation line or pipe R2 to the first ventilation line R1 at a portion near the carbon canister 2, and additionally the inside of the storage tank 1 is connected through the second ventilation line R2 and the partition valve 4 to the first ventilation line R1. This allows gasoline vapor generated during fuel supply to be fed into the carbon canister 2. The second ventilation line R2 extending into the storage tank 1 is provided at its lower end with a float valve 5.
The carbon canister 2 is connected through a purge line or pipe R3 and through a vacuum introduction line R4 with an air intake pipe K of an engine E. Under the suction of intake vacuum during running of the engine E, air is sucked into the carbon canister 2 from an atmospheric air inlet 2a so as to purge gasoline vapor adsorbed in the activated carbon in the carbon canister 2. The purged gasoline vapor is sucked into the air intake pipe K. This is a so-called purge mechanism for gasoline vapor.
Now, regulation for exhaust gas emission control of automotive vehicles tends to be stricter from the viewpoint of environmental protection. Besides, combustion control in an engine of the automotive vehicle has been highly sophisticated for the purpose of improving fuel consumption and drivability (such as response and fidelity) of the engine. In view of these, the following difficulties have been encountered in the above-discussed conventional emission control system: Since gasoline vapor retained in the carbon canister is fed to the engine to be burned, air-fuel ratio of air-fuel mixture to be fed into the engine unavoidably gets out of order thereby making impossible to attain the above purpose. In contrast, if a control is made intending to suppress a change in air-fuel ratio, restoration of performance (or purge of gasoline vapor) is unavoidably retarded so that the carbon canister retains excess gasoline vapor which is to be discharged out of the carbon canister 2 from the atmospheric air inlet 2a of the carbon canister 2.